Spark plug



H. P. SPARKES Dec. 5, 1939.

SPARK PLUG Filed Sept. 29, 1958 INVENTOR flqeer/ libvekis Patented Dec. 5,. 1939 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to spark plugs for internal combustion engines, and in particular to the construction of the shell to effect heat radiation and mechanical compensation. 7

It is well recognized that spark plugs become overheated when in use in modern high compression engines, and that this overheating greatly reduces the efliciency of the plug and shortens its life. The overheating furthermore causes undue mechanical expansion and consequent strain which loosens the parts of the plug, causing it to become leaky or to develop fractures. This difficulty is especially apparent in aviation work, and requires the constant replacement of very expensive plugs which are used in considerable quantities. For instance, a modern transport ship with two motors has fifty-six plugs constantly in use which cost approximately three to four dollars each, or more.

It is the purpose of this invention to provide these plugs with an eflicient radiating means which definitely eliminates the overheating of the plug, and all of the consequent damage connected therewith, and at the same time to effect a thermal compensation in the shell of the plug which avoids the mechanical strains which result in a loosening or fracture of the plug. Both of these accomplishments greatly increase the efliciency and lengthen the life of the plug.

The means of accomplishing these results is to provide a plug shell with its internal wall made from the usual steel alloy, and an external wall joined integrally thereto, made from copper or other material of high thermal conductivity.

The means of producing such a thermal compensating and heat dissipating element is thoroughly disclosed in my pending applications, Serial No. 138,873, and Serial No. 207,647.

As is disclosed in my allowed application Serial No, 138,873, a steel ingot or casting is provided of suitable shape and size, and after this ingot is pickled, it is brought up to a temperature greater than the melting point of copper and placed in a suitable mold, whereupon molten copper is poured around it to form the heat-dissipating jacket. Another method is to provide a copper shell which may or may not be finished to its ultimate form, into this copper shell molten ferrous metal is poured; the temperature of this molten metal being great enough to melt into the copper causing a fusion which resultsin a heterogeneous mixture of the ferrous and cuprous materials. Another method of producing an article wherein it is desired to have'two or more metals molecularly joined into a single unit is described in my pending application Serial No. 207,647. This invention contemplates the union of two or more metals by pre-mixing said metals in their proper proportions, then melting the whole into a homogeneous mass, and then the separating of the metals according to their relative specific gravities by a centrifuging method. I have found that castings made according to this centrifuging process are entirely free from blow holes caused by gases formed in the molten metal. This advantage is due to the fact that the whirling of the molten mixture squeezes the gases out of the metal and drives them toward the center of the mass, where they bubble oil. In order to insure sufficient heat to retain the metals in the liquid state long enough to permit the movement of the heavy molecules to the outer edge when whirled, I have found that a high frequency electric coil surrounding the mold produces enough heat to maintain this liquid state as long as the current is applied. Another method of melting the metals consists of placing oxide of iron and copper preferably in a powder or granulated form into a funnel shaped crucible which is provided with a discharge port in the bottom, and adding a suificient aluminum powder which when oxidized causes a heat suflicient to melt the oxide of iron and copper.

In order that the details of construction may be more clearly understood, reference is made to the accompanying drawing, in which:

Figure 1 is an elevation partly in section, showing a spark plug with the radiating fins.

Figure 2 is an elevation partly in section, showing the radiating fins carried throughout the full length of the plug.

Figure 3 is an end view of Figure 1.

Similar reference numerals refer to similar parts throughout the drawing.

In the drawing, I is a threaded bushing adapted to be screwed into the engine. 2 is a multiple pronged terminal fastened in the end of the bushing I. 3 is an electrode adapted to be centralized in the terminal 2. The electrode 3 is supported on a shaft 4. Mounted on the shaft 4 and adjacent the electrode is a series of mica insulation washers 5 which form a'cone-shaped arrangement. Mounted on the shaft 4 and forced tightly against the mica washers 5 is a tapered brass plug 8 This plug is designed to seat into the main body portion of the spark plug, which consists of a threaded bushing I which screws into the threaded portion I, a hexagon nut'i'formed inteare formed a series of thin radiating fins l0, and a cylindrical threaded terminal H.

The inside of this main body portion is bored out at I2 to receive the outer end of the shaft 4. Over the end of the shaft 4 are pressed 2. series of mica washers l3 which act to insulate the shaft 4 from the cylindrical barrel 9. Likewise, the plug 6 is insulated from the shaft 4 by mica insulations l4. The shaft 4 is curled over at the end I5 to press against the mica washers l4 and holds them firmly in place. To carry the current from the distributor head (not shown) into the spark plug, a spring I6 carrying a contact head I'I, is'inserted in the barrel 9, and of course is insulated by the mica lining 2|. A standard ignition wire 18 is placed with its end abutting the contact H. In order to hold the ignition wire I8 firmly in place, a threaded sleeve I9 is screwed onto the terminal ll of the main body. In' order to further prevent the breaking of the ignition wire on making a turn into the plug, a goose-neck lead tube 20 is held in place by the sleeve 19 which thoroughly protects the ignition wire at that point.

Referring again to the part 9 on which this I0 are formed, this part constitutes the principal feature of my invention. The barrel 9, for mechanical strength, is preferably made of steel, and the fins ID are joined thereto by fusion in accordance with the subject matter of my previous applications, Serial Nos. 138,873, and 207,647. I prefer to make the barrel 9 of steel and the fins III of copper, the one being fused continuously to the other. By this arrangement, I have provided an internal wall which has great mechanical strength and low thermal conductivity, and this wall being on the inside and nearest the plug parts, receives the larger amount of heat transmitted from the engine through the plug. The copper'jacket surrounding this wall 9, being of a material of high thermal conductivity and relatively low mechanical strength, acts to radiate the heat inducted into the barrel 9. Furthermore, the expansion caused by the heat of the barrel 9 is compensated by the expansion due to the heating of the fins l0 and web IDA joining them together.

As disclosed in my previous applications, the construction produces a rigid member which is thoroughly compensating without mechanical movement or distortion. Many of the plug failures are caused by excessive heating of the plug due to lack of sufficient radiation, and distortion of the plug members due to unequal expansion.

In a spark plug of the type shown in Figure 1,

where there are a number of points, such as indicated by 2, positioned around a central electrode 3, it is very necessary to maintain a precise accuracy in order to have the plug function properly. Excessive heating of the plug barrel very often causes a displacement of the central electrode, indicated as 3, with respect to the electrode 2.

Obviously, the fins may be arranged to radiate the heat from any portion of, the plug, and a modified form is shown in Figure 2, wherein the radiating fins are carried below the nut section shown in Figure l.

The present invention so radiates the heat and compensates against distortion of the plug body that this central electrode 3 is maintained at an accurate position with respect to the electrodes 2 at all times.

Having described the invention, what I claim as new and desire to secure by Letters Patent is:

1. In a spark plug, a body portion adapted to be fastened into an opening in the engine, one or more electrodes mounted on the said body portion, a central electrode mounted in the said body portion, and a finned radiating jacket of high thermal conductivity fused to the said body portion.

2. In a spark plug. a tubular body portion adapted to be fastened into an opening in the engine, a copper-radiating jacket fused to the said body portion, an electrode mounted within the said body portion and insulated therefrom, and co-acting electrodes projecting from the said body portion.

3. In a spark plug, a tubular body portion adapted to be fastened into an opening-in the engine, a copper finned radiating jacket fused to the said body portion, an electrode mounted within the said body portion and insulated therefrom, and co-acting electrodes projecting from the said body portion.

4. In a'spark plug, a body portion made from a material of low thermal conductivity and low coefficient of expansion, adapted to be fastened into an opening in the engine, one or more electrodes mounted on the said body portion, a central electrode mounted in the said body portion and insulated therefrom, and a finned radiating jacket of high thermal conductivity and high co-eflicient of expansion fused to the said body portion.

HARRY P. SPARKES. 

